Glass Knifefish

Eigenmannia virescens

Also known as Green Knifefish, Virescens Knifefish

Animalia›Chordata›Gymnotiformes›Sternopygidae

The Glass Knifefish is a sleek, transparent freshwater fish native to South America, prized for its unique appearance and graceful swimming behavior. Despite their delicate appearance, they are hardy fish that thrive in well-maintained aquariums with plenty of open swimming space. They are nocturnal and peaceful, making them excellent additions to community tanks with similarly-sized, non-aggressive fish.

Where it's from

Native to the Amazon, Approuague, Arroio do Conde, Arroio do Petim and 49 other river basins

Brazil, French Guiana, Argentina, Colombia, Panama, Bolivia, Venezuela, Suriname and 5 more

At a glance

Size: 6 in; 15 cm
Min tank: 40 gal; 151 L
Temp: 75–82°F; 24–28°C
pH: 6.0-7.5
GH: 71–143 ppm; 4–8 dGH
Temperament: Peaceful
Swims: Middle
Lifespan: 8-10 yrs

Ammonia 0 ppm and nitrate under 20 ppm.

Care

Diet

Glass Knifefish are carnivorous and prefer small live foods such as bloodworms, brine shrimp, and small insects. They will also accept high-quality frozen foods and small pellets. Feed once or twice daily in amounts they can consume within a few minutes, as they are nocturnal feeders and may be shy during the day.

Behavior

Glass Knifefish are primarily nocturnal and spend much of the day hiding among plants and decorations. They are peaceful fish that swim gracefully through the water column, often moving in a distinctive undulating pattern. They are solitary or can be kept in small groups, though they may exhibit mild territorial behavior toward each other.

Breeding

Breeding Glass Knifefish in captivity is extremely difficult and rarely achieved in home aquariums. They require very specific water conditions and environmental triggers that are challenging to replicate. Most specimens available in the aquarium trade are wild-caught, and breeding information remains limited.

Tank mates

See all 5

Neon Tetra

Small, peaceful schooling fish that occupy different water zones

good

Cardinal Tetra

Similar size and temperament, peaceful community fish

good

Dwarf Gourami

Peaceful surface-dwelling fish with minimal interaction

good

Otocinclus

Small algae eaters that are peaceful and occupy bottom zones

excellent

Rummy Nose Tetra

Peaceful schooling fish that coexist well in community settings

good

Fits a 40-gallon tank Peaceful

No state or federal restrictions on record.

Not legal advice, and possibly incomplete or out of date. Rules vary by state and change over time; check with your state wildlife or agriculture agency before buying, keeping or shipping it.

The care information here is written with AI help, so it can contain mistakes. Spot one? Tell us and we'll fix it. Native range: Catálogo Taxonômico da Fauna do Brasil (CC BY 4.0); Lista Roja de la Fauna Venezolana 2015 (CC BY 4.0); Tedesco et al. 2017 (CC0).